Various resin compositions that can be cured by light (e.g. ultraviolet rays) have been used in inks, coating materials, adhesives, photoresists, and other applications. For example, UV curable printing inks are highly valued because, e.g., they have a high cure rate so that they can be cured in a short time; they are environmentally friendly due to no use of solvents; and they can save resources and energy. Therefore, they are increasingly widely used in practice.
Among such resin compositions, those containing diallyl phthalate resins derived from diallyl phthalate (diallyl orthophthalate, diallyl isophthalate, or diallyl terephthalate) are used as UV offset inks for paper.
However, in offset ink applications, the incorporation of diallyl phthalate resins is known to result in insufficient adhesion to plastic substrates (see, for example, Patent Literature 1). These days, products of various types of plastic materials, including polyethylene terephthalate (PET) and polypropylene (PP), are on the market. Thus, there is a need to improve adhesion to plastic substrates with which diallyl phthalate resins have problems.
Patent Literature 2 describes that, among active energy ray-curable ink compositions each containing a photopolymerizable acrylate monomer, a pigment, a photoinitiator, and a petroleum-based resin which is soluble in the photopolymerizable acrylate monomer, those containing specific petroleum-based resins have excellent transferability and adhesion to olefin resin films such as polyethylene or polypropylene films. However, these active energy ray-curable ink compositions have a versatile problem in that the diallyl phthalate resins are compatible with limited petroleum-based resins.